1. Field of the Invention
This invention relates generally to the formation of laminate circuit structures by photolithographic techniques, and more particularly to a method of forming composite laminate structures which utilizes a multiplicity of preformed circuits having signal and voltage planes and a laminate structure having a ground plane without signal planes.
2. Related Applications
This application is related to application Ser. No. 09/203,956, Filed Dec. 2, 1998 Entitled xe2x80x9cTwo Signal One Power Plane Circuit Boardxe2x80x9d and application Ser. No. 09/203,978, Filed Dec. 2, 1998 Entitled xe2x80x9cMulti-Voltage Plane, Multi-Signal Plane Circuit Cardxe2x80x9d.
A conventional technique of forming a laminate circuit board structures includes forming layers of dielectric material and electrically conducting material to provide multiple layers of circuits and voltage planes. Voltage planes can be either ground plane or power plane, and are sometimes collectively referred to as power planes. In one prior art technique of forming such structure, layers of dielectric material and conducting material successively applied, i.e. the dielectric material is applied and then voltage planes are supplied thereon and if necessary through holes formed by the drilling or etching of through holes or blind vias. This technique relies on each successive step adding additional structure and the circuitry layers are formed individually; i.e., in each step in forming the signal planes the planes are formed after the formation of the prior layer of signal plane and forming the signal plane on formed power planes. This requires precession drilling to form the plated through holes all of which is time consuming, especially where there is a large number of drilled holes required to form plated through holes.
Thus it is desired to provide a relatively inexpensive photolithographic technique of forming a composite laminate structure from individual discrete laminate structures into a composite laminate- structure.
A method forming a composite laminate structure includes providing first and second circuit board element each having circuitry on at least one face thereof and plated through holes. A voltage plane element is provided having at least one voltage plane having opposite faces with layers of partially cured photodielectric material on each face. At least one hole is photopatterned and etched through the voltage plane element but completely isolated from the voltage plane. Each through hole in the voltage plane element is aligned with a plated through hole in each of the circuit board elements to provide a surface on the voltage plane element communicating with the plated through holes. The voltage plane is laminated between the circuit board elements and the photoimageable material on the voltage plane is fully cured. The surfaces of the voltage plane element communicating with the plated through holes in the circuit board elements are plated with a conducting material to establish a connection between the circuitry on the first and second circuit board elements.